Starters comprising double contact electromagnetic contactors are known in the state of the art. Such a starter la according to the prior art, including a contactor 10a, is described below with reference to FIG. 1.
The contactor 10a comprises a housing 104 in which a plunger core 100 moves in a translatory manner, the front end 101 of which is provided with a finger 1010. The rear end of the plunger core 100 actuates two moving contact plates CM1 and CM2, designed to establish galvanic contact between contact terminals C11, C12 and C21, C22. A core return spring 103 is disposed between the housing and the front end 101 of the plunger core 100 and exerts a restoring force counteracting a translatory movement of the latter towards the rear.
The contactor 10a also comprises two windings, Lm and La, having a common end. Another end of the winding Lm is connected to an electrical mass M (conventionally the chassis of the vehicle). Another end of the winding La is connected to the terminals C12, C22 and an electrical brush B1. The end common to both windings Lm and La is connected to the positive terminal (“B+”) of a battery 12 via a starting contact 13 of the vehicle (or any element acting in a similar way). The terminal C11 is directly connected to the positive terminal B+ of the battery 12. The terminals C21 is connected to the positive terminal of the battery 12 through a current limit resistance RD.
The starter 1a comprises an electric motor 11. This motor 11 traditionally consists of an armature or rotor 110 (winding L3) and an inductor or stator 114 which can comprise permanent magnets. The armature 110 is conventionally energised via a collector ring 115, disposed at the rear of the motor 11, and two brushes B1 and B2, the brush B1 designated positive being connected to the terminals C12, C22 and the brush B2 designated negative being connected to the mass M.
A starter is disposed in front of the motor 11, said starter here comprising a starter gear unit 113, free wheel 112, meshing spring 115 and a pulley (not referenced) in which a fork 15 is engaged. A spiral ramp 111 is also provided in front of the motor 11. The contactor 10a and the motor 11 are mechanically coupled by the fork 15 moving around an axis of rotation Δ1. As it appears in FIG. 1, the upper end of this fork 15 is carried along by the finger 1010. The lower end of the fork 15 is mechanically coupled in the region of the starter pulley at the rear of the engagement spring 115, itself disposed between this lower end and the free wheel 112.
When the driver of the vehicle actuates the starting contact 13, the electric current then circulates in the windings Lm and La of the contactor 10, the connection to the mass M of the winding La being through the motor 11. An electromagnetic force then builds up in the contactor 10a which causes the core 100 to be attracted to the rear (arrow f1). The spring 103 is compressed and exerts a counteractive restoring force. The plunger core 100 drives the fork 15 rotationally around the axis Δ1 and the lower end of the latter in its turn drives the spring unit 115, free wheel 112 and gear 113 forwards (arrow f2).
When the plunger core 100 of the contactor 10a reaches an intermediate point in its travel, the moving contact plate CM1 short-circuits the contact terminals C11 and C12 (closed position), the contact terminals C21 and C22 themselves remaining not short-circuited (open position). The contact terminals C11 and C12 in the closed position, through the current limit resistance RD, connect the positive brush B1 to the positive terminal B+ of the battery 12 and energise the motor 11, the electrical circuit being closed again by the negative brush B2. The armature 110 (rotor) of the motor 11 starts to turn around its axis of rotation Δ2 with reduced power, that is to say, at reduced speed and torque, due to the current being limited by the resistance RD, which also causes a rotation R of the gear 113. Set in motion by a double translational (arrow f2) and rotational R movement, the gear 113 approaches the toothed crown 14 of the thermal engine.
In a more precise way, two cases can then occur:
1) The gear 113 directly meshes with the crown 14 in its translational movement (arrow f2) and the plunger core 100 will continue its translational movement until it reaches the end of its travel.
2) A tooth of the gear 113 butts against a tooth of the crown 14, which also tends to block the travel of the plunger core 100. The starter spring 115 allows the plunger core 100 to continue its advance, since this spring 115 is compressed, the pulley being able to slide on the shaft. The drive of the gear 113 by the motor 11 at reduced speed prevents damage to the teeth of the gear 113 and of the crown 14 on account of a so-called “milling” effect. As a result of its rotational and translational movements, the gear 113 ends up meshing with the crown 14 and the plunger core 100 continues its translational movement until it reaches the end of its travel.
When the plunger core 100 of the contactor 10a has reached the end of its travel, the moving contact plate CM2 short-circuits the contact terminals C21 and C22 (closed position), the contact terminals C11 and C12 remaining in the closed position. The contact terminals C21 and C22 in the closed position directly connect the positive brush B1 to the positive terminal B+ of the battery 12. The motor 11 is then supplied with full power and turns the thermal engine for a starting operation.
In the situation above, the pull-in winding La is short-circuited since there is no longer any difference in potential between the end common to both windings, Lm and La, and the contact C21-C22 are both connected to the positive terminal of the battery 12. The moving contact plates CM1 and CM2 are held in the closed position by the holding winding Lm, acting upon the plunger core 100 and the core return spring 103.
When the driver breaks the starting circuit by opening the starting contact 13, the electromagnetic force which has been building up in the contactor 10a ceases, the holding winding Lm no longer being energised. The plunger core 100 is returned to its rest position by the spring 103 and the electrical connection between battery 12 and motor 11 is broken. The motor 11, no longer being energised, ceases to turn the gear 113. Moreover, since the plunger core 100 returns to its initial position (towards the rear), it acts upon the fork 15 which disengages the gear 113 from the crown 14.
On the other hand, if the driver maintains the starting contact 13 in the closed position longer than necessary, the thermal engine of the vehicle starts to operate, the gear 113, therefore the armature 110 of the motor 11, is consequently subjected to a very high rotational speed (typically, in the case of a thermal engine rotating at 3,000 rpm, the rotational speed of the gear will reach 25,000 rpm, the reduction gear ratio between “crown-motor” generally ranging between 8:1 and 16:1). To prevent the centrifugation of the motor 11, it is therefore necessary to disconnect the starter shaft from the gear 113. This is the role allocated to the free wheel 112.
In the contactor 10a of FIG. 1, closing of the contact C11-C12 prior to that of the contact C21-C22, allowing the motor 11 to function in two distinct modes of operation as described above, is introduced by different tarings of contact springs P1, P2 and P3.
This prior art solution is satisfactory overall. However, it is desirable to propose improvements offering additional degrees of freedom in the design of a starter of the type described, particularly in terms of controlling the interval between closing of the contacts during a starting operation.